The Influence of Direct Thrombin Inhibitors on the Formation of Platelet-leukocyte Aggregates and Tissue Factor Expression

Introduction

High concentrations of platelet-monocyte aggregates (PMAs) have been found in patients with myocardial infarction (MI). Oral direct thrombin inhibitors (DTIs) are under evaluation as long-term antithrombotic treatment. The aim was to evaluate whether DTIs affect the formation of platelet-leukocyte aggregates, TF expression and procoagulant microparticles (MPs).

Material and Methods

DTIs were added to an experimental whole blood model before platelet activation with thrombin or ADP. The concentrations of PMAs, platelet-granulocyte aggregates (PGAs), the amount of platelets bound per leukocyte and MPs were investigated by flow cytometry. TF mRNA and activity were recorded in all settings. TF activity was evaluated in a MI population treated with or without an oral DTI.

Results

In vitro, thrombin and ADP increased the formation of PMAs and PGAs as well as TF mRNA expression. DTIs reduced the amount platelets bound to monocytes (p = 0.02) and to granulocytes (p = 0.001) upon thrombin stimulation together with a reduction of TF mRNA. In contrast, the ADP-induced formation of PMAs, PGAs and TF mRNA was not affected by the DTIs. Both thrombin and ADP stimulation increased the amount of TF-expressing MPs, which was effectively inhibited by the DTIs (p = 0.02-0.002). In the MI population, the DTI reduced the TF activity (p < 0.001).

Conclusion

DTIs modulate the formation of PMAs, PGAs and the TF production therein. Together with a reduction of procoagulant MPs, these results may contribute to the clinical benefit found of oral DTIs. Targeting different mechanisms in platelet and coagulation activation may be of importance due to the lack of effect of DTIs on ADP-induced platelet-leukocyte aggregates and TF production.     

Murine strain differences in hemostasis and thrombosis and tissue factor pathway inhibitor

Introduction

Differences among murine strains often lead to differential responses in models of human disease. The aim of the current study was to investigate whether differences exist among strains in models of hemostasis and thrombosis and whether these differences are reflected in differences in the tissue factor (TF) pathway.

Methods

We examined baseline hemostatic parameters and the response to FeCl3-induced arterial thrombosis and a tail vein bleeding model in C57BL/6J (C57), 129S1/SvImJ (129S), and Balb/cJ (BalbC) mice. Finally, we examined TF and tissue factor pathway inhibitor (TFPI) activities in blood and expression in vascular tissue to determine whether these factors covary with a thrombotic phenotype.

Results

No differences were observed in PT or aPTT among strains. 129S mice had lower platelet counts (p < 0.001). BalbC had an increased rate of occlusion (mean occlusion time of 330 ± 45 sec) in a FeCl₃-induced model of thrombosis when compared to C57 (1182 ± 349 sec) or 129 S (1442 ± 281 sec) (p < 0.05). Similarly, BalbC demonstrated reduced blood loss in tail bleeding experiments when compared to C57 and 129S. Vascular expression of TF and TFPI content did not correlate with the thrombotic phenotype of BalbC. However, circulating TFPI activities were lower in BalbC compared to both C57 and 129S mice. When normalized to circulating TF activities, BalbC had lower circulating TFPI activity than C57 and 129S, and there was a significant correlation between tail bleeding and normalized TFPI activity (r = 0.67).

Conclusions

These data suggest that there are significant differences among strains in thrombosis and hemostasis and that circulating TFPI activity correlates with these differences.     

Increased thrombin generation in inflammatory bowel diseases

Background

Inflammatory bowel diseases (IBD) are characterized by an increased thrombotic risk of uncertain etiology. Endogenous thrombin potential (ETP), a parameter of the thrombin generation curve, represents a new tool in the evaluation of thrombotic and bleeding disorders.

Aims

To study ETP in IBD patients and to correlate the results with clinical and biochemical features.

Methods

Seventy-four IBD patients (37 ulcerative colitis and 37 Crohn's disease) and 74 sex- and age-matched healthy individuals. ETP was measured upon activation of coagulation with small amounts of tissue factor and phospholipids in the presence or absence of thrombomodulin; results were expressed as nM thrombin·minutes.

Results

Mean±SD ETP values were significantly higher in patients (1,499 ± 454) than controls (1,261 ± 385) (p < 0.001) only when the test was performed in the presence of thrombomodulin. ETP evaluated as ratio (with/without thrombomodulin), taken as an index of hypercoagulability, was significantly higher in patients (0.69 ± 0.14) than controls (0.62 ± 0.18) (p < 0.006). Patients with increased C-reactive protein (CRP) had significantly higher mean ETP (1,721 ± 458) than those with normal CRP (1,357 ± 394) or controls (1,261 ± 385) (p < 0.001). Patients who at the time of blood sampling were classified as having a clinically active disease had ETP higher than those who were quiescent (1,655 ± 451 versus 1,388 ± 427, p < 0.001) or controls (1,261 ± 385, p < 0.001).

Conclusions

ETP measured in the presence of thrombomodulin or as ratio (with/without thrombomodulin) is increased in IBD patients, mainly in those with increased CRP or active disease. It may be considered as a candidate test for prospective studies aimed at assessing the risk of thrombosis in IBD patients.     

Aging is associated with impaired thrombus resolution in a mouse model of stasis induced thrombosis

Introduction

To evaluate the effects of aging on venous thrombosis.

Material and Methods

Anesthetized male mice (C57BL/6, n = 125) underwent complete inferior vena cava occlusion to produce venous thrombosis. Experimental groups included 11-month-old mice (OLD), 2-month-old mice (YOUNG), and age-matched non-thrombosed controls. Mice were euthanized and the following parameters were evaluated two days post-thrombosis: thrombus mass (grams/cm), vein wall inflammatory cells (cells per 5 high powered fields), active plasma plasminogen activator inhibitor-1 (PAI-1, ng/mL), vein wall P-selectin protein determination by ELISA (pg/mL), circulating plasma microparticles (MPs, MPs/200 µL), MP tissue factor (TF) activity (pM), and in vivo MP re-injection experiments.

Results

Thrombosed OLD mice had greater thrombus mass than YOUNG mice (389 ± 18 vs. 336 ± 14 g × 10^− 4/cm, P < .05). OLD mice had decreased vein wall monocyte, lymphocyte, and total inflammatory cell populations versus YOUNG mice (P < .05). Vein wall P-selectin levels were greater in OLD thrombosed mice versus YOUNG (7306 ± 938 vs. 3805 ± 745 pg/mL, P < .05). Active plasma PAI-1 concentrations were increased in OLD mice versus YOUNG thrombosed animals (20 ± 4 vs. 8 ± 2 ng/mL, P < .05). OLD mice had significantly higher circulating leukocyte-derived MPs versus YOUNG mice (5817 ± 850 vs. 2563 ± 283 MPs/200 μL PPP, P < .01). OLD mice had plasma MPs with increased TF activity versus YOUNG animals post-thrombosis (34 ± 4 vs. 24 ± 2 pM, P < .05). Finally, YOUNG recipient animals, whether re-injected with OLD or YOUNG donor MPs, had a significant increase in thrombus mass versus OLD recipient animals (P < .01).

Conclusion

Aging influenced several circulating and vein wall factors that decreased thrombus resolution in older animals compared to younger ones in our mouse thrombosis model.     

Endogenous thrombin potential (ETP) in plasma from patients with AMI during antithrombotic treatment

Background

The beneficial impact of warfarin in preventing new events after AMI is well established. Decrease in thrombin generation seems to be the key element in anticoagulant treatment.

Objectives

The aims were to investigate the effect of warfarin and platelet inhibition on thrombin generation, assessed by the endogenous thrombin potential (ETP), and study the relation between coagulation parameters and ETP in patients with AMI.

Patients/Methods

In the present sub-study of the WARIS II trial, patients with AMI were randomly assigned to treatment with aspirin 160 mg/d (n = 57), aspirin 75 mg/d and warfarin (INR 2.0-2.5) (n = 68) or warfarin (INR 2.8-4.2) (n = 61). Fasting blood samples were collected from patients at discharge from hospital and after 6 weeks treatment.

Results

Correlation analyses showed that both ETP and peak thrombin levels were significantly correlated with Factor VII Ag (r = 0.38 and 0.36 respectively, p < 0.01 for both) and with F1+2 (r = 0.26 and 0.23 respectively, p = 0.01 for both) at baseline. Antithrombotic treatment for 6 weeks caused a highly significant inhibition of ETP in patients treated with warfarin (− 28% ± 5%, p < 0.001), and patients treated with aspirin/warfarin (− 24% ± 8%, p = 0.04). Similarly, peak thrombin levels were reduced in patients treated with warfarin (− 18% ± 7%, p = 0.049) and aspirin/warfarin (− 19% ± 5%, p = 0.029), whereas an increase (12% ± 4%, p = 0.029) occurred during aspirin treatment alone. F1+2 levels decreased by 64% and 58% in the warfarin and aspirin/warfarin groups, respectively (p = 0.001 for both).

Conclusions

In patients with AMI, warfarin significantly reduced the endogenous thrombin generation and the potential to generate thrombin in plasma ex vivo, whereas aspirin alone had no effect on thrombin generation in vivo or ex vivo, assessed by ETP.     

Tissue factor-induced Thrombin Generation in the Fasting and Postprandial State among Elderly Survivors of Myocardial Infarction

Introduction

Tissue factor (TF)-induced thrombin generation (TG) ex vivo has been suggested to be an important method to assess thrombotic risk. No studies have investigated the impact of postprandial lipemia on TF-induced TG. Since myocardial infarction (MI) is associated with elevated postprandial levels of triglycerides, we hypothesized a differential impact of postprandial lipemia on coagulation activation in MI-patients and healthy controls.

Material and Methods

Elderly survivors of acute MI (n = 44) and healthy age-and sex matched controls (n = 43) underwent a fat tolerance test (1 gram per kg body weight) to assess coagulation activation during postprandial lipemia.

Results

The incremental area under the curve (AUCi) for serum triglycerides was higher in MI-patients than in healthy age-and sex matched controls (5.64 ± 0.52 mmol/L?h and 3.94 ± 0.39 mmol/L?h, p = 0.012) during the postprandial phase. Subsequent endogenous activation of coagulation, assessed by FVIIa and thrombin generation (F1 + 2), was similar among groups and not related to levels of triglycerides during the postprandial phase. Healthy individuals had a gradual decline in TF-induced thrombin generation ex vivo, assessed by endogenous thrombin potential (ETP) (AUCi = - 542.4 ± 71.4 nM?min?h, p < 0.001), whereas MI-patients retained their ETP (AUCi = 127.4 ± 89.0 nM?min?h, p = 0.47) in plasma during the postprandial phase (p for group difference = 0.005).

Conclusions

MI-patients had elevated postprandial lipemia and retained their ability for TF-induced TG in plasma ex vivo in the postprandial phase, whereas the capacity gradually decreased in healthy individuals. Further studies are warranted to reveal underlying mechanism(s) and clinical implications.     

Circulating activated factor XI and active tissue factor as predictors of worse prognosis in patients following ischemic cerebrovascular events

Background

Elevated factor (F)XI is associated with an increased risk for ischemic stroke. Activated FXI (FXIa) and tissue factor (TF) have not been studied following stroke. The aim of the current study was to evaluate circulating FXIa and TF in patients with prior cerebrovascular events.

Patients/Methods

We studied 241 patients, including 162 after ischemic stroke and 79 after transient ischemic attack (TIA), recruited 6 months to 4 years (median, 36 months) after the events. Plasma TF and FXIa activity following the index event were determined in clotting assays by measuring the response to inhibitory monoclonal antibodies.

Results

Active TF was detected in 25 (10.4%) of the patients, while FXIa activity (median, 37.5 [IQR 397] pM) was found in 64 (26.7%) of the patients (p < 0.01). The prevalence of active TF and FXIa was higher in subjects with previous stroke compared with those with a history of TIA (13% vs 5.1%, p = 0.05, and 34% vs 11.4%, p < 0.0001, respectively). Patients with circulating FXIa were younger and had higher fibrinogen and interleukin-6 compared to the remainder. Patients with detectable TF or FXIa activity had higher NIHSS score, higher modified Rankin scale and lower Barthel Index than the remaining subjects (all p < 0.05).

Conclusion

Circulating active TF and FXIa can occur in patients with cerebrovascular ischemic events ≥ 6 months after the events. The presence of these factors is associated with worse functional outcomes, which highlights the role of persistent hypercoagulable state in cerebrovascular disease.     

Pioglitazone inhibits platelet function and potentiates the effects of aspirin: a prospective observation study

Background

Thiazolidinediones (TZDs) are agonists of PPARγ and exert beneficial metabolic effects in patients with diabetes. They may also affect platelet function.

Objectives

To characterize potential platelet inhibitory effect of pioglitazone alone and in the presence of aspirin.

Methods

20 normal and 20 diabetic subjects were enrolled in a prospective study. On day 1, a blood sample was obtained at baseline and a second one after ingestion of 30 mg of pioglitazone. PRP was prepared and platelet aggregation and release were evaluated using ADP, collagen and arachidonic acid as agonists. Subjects returned at 6-9 days later after ingesting a single 81 mg dose of aspirin and a third blood sample was obtained. The subjects then again ingested 30 mg of pioglitazone and a fourth and final blood sample was obtained. Platelet aggregation and release were measured. PRP was incubated with thrombin to activate platelets, and the serum was separated and assayed for thromboxane B2, TGFβ and CD40L

Results

Pioglitazone alone did not affect aggregation with arachidonic acid. However, following ingestion of both aspirin and pioglitazone aggregation was significantly decreased compared to aspirin alone (P < 0.0001). Pioglitazone also potentiated aspirin-induced inhibition of ATP release using either arachidonic acid or collagen. Following pioglitazone alone, TXB₂ release was 32,719 ± 3,585 pg/ml which was significantly reduced compared to baseline (42,075 ± 4,479, P = 0.0004). Pioglitazone also potentiated the inhibition of TXB₂ release by aspirin.

Conclusion

Pioglitazone inhibits platelet function and potentiates the inhibitory effects of aspirin.     

Evaluation of recurrent venous thromboembolism in patients with Factor V Leiden mutation in heterozygous form

Introduction

To evaluate the risk for recurrence after first venous thromboembolism (VTE) among patients with or without Factor V Leiden (FVL) mutation.

Materials and Methods

A prospective population based study of 1465 consecutive unselected VTE patients was performed at Skåne University Hospital 1998-2008. The VTE was objectively verified and the patients answered questionnaire and left blood samples for evaluation.

Results

Out of 1465 patients (721[49%] men and 744[51%] women) thrombophilia data were available for 1267, and FVL mutation was found in heterozygous form in 339 (27). The homozygous form and prothrombin mutation (PTM) were much less common. Patients were followed during 4.8 ± 2.3 years (total 6133 patient years) and recurrence after first VTE (evaluated in 1108 patients) occurred in 131 (12%, 95%CI 10-14%), where of 49(37%) had heterozygous FVL mutation and 57(44%) were without thrombophilia. The remaining 25(19%) patients had either PTM, FVL in homozygous form, compound PTM/FVL or unknown thrombophilia status. Having FVL mutation in heterozygous form significantly increased the risk for VTE recurrence (odds ratio 2.4 (95 %CI 1.6-3.6; p < 0.01). In a Kaplan-Meier analysis the FVL group also differed significantly (p < 0.01) from the other patients concerning time to recurrence (almost 25% vs. 10% after 8 years).

Conclusions

FVL mutation in heterozygous form is common among VTE patients and significantly increases the risk for VTE recurrence.     

Increased thrombin generation in women with a history of preeclampsia

Introduction

Women with a history of preeclampsia have an increased risk for cardiovascular disease in later life. We evaluated thrombogenic characteristics of women with a previous history of preeclampsia, expressed in levels of thrombin generation, number of microparticles and related to menstrual cycle and endothelial function, measured as flow-mediated dilatation.

Materials and methods

We included 18 primipara women with a history of preeclampsia and 17 healthy primipara controls, 15 (± 3) months after the index pregnancy. Thrombin generation was measured by tissue factor triggered assay, microparticle levels were measured by flow cytometry and the endothelial function was previously examined by measuring flow-mediated dilatation by high-resolution ultrasound, during follicular and luteal phases of the menstrual cycle.

Results

Women with previous preeclampsia produced more total amount of thrombin as calculated from thrombin max, thrombin potential and max slope levels p < 0.05, 0.01 and 0.01 respectively. Platelet derived microparticle levels were higher in women with a history of preeclampsia, p = 0.07. Flow-mediated dilatation was significantly decreased in comparison to healthy controls (p < 0.0001). There were no variation in levels of thrombin, microparticles and flow-mediated dilatation during the menstrual phases.

Conclusion

Women with a history of preeclampsia show signs of hypercoagulability as indicated by higher thrombin generation and higher platelet derived microparticle levels. Since these women were investigated more than one year after delivery, these results may be indicative of an increased risk of cardiovascular events later in life.     

Behavioral and psychological symptoms of dementia in a pilot psychogeriatric unit: management and outcomes

Background

Behavioral and psychological symptoms in dementia (BPSD) are a major concern. The French government gave a consensual definition of reinforced intermediate-term care units for BPSD within the project “Plan Alzheimer 2008/2012”.

Objective

Our aim was to report one of the first experiences of this unit in France.

Results

Fifty-two patients (38 females, 14 males) were included, mean age 82.07 ± 7.84 (73-97). About 80% of patients were improved and there was a high discharge rate to home of about 30%. Night-time behaviors, aberrant motor behaviors and agitation were the most frequent symptoms.

Conclusion

Our study confirms that demented elderly patients greatly benefit from a specific BPSD care unit in agreement with the objective of Plan Alzheimer 2008/2012.     

Coagulation parameters in patients receiving dabigatran etexilate or rivaroxaban: two observational studies in patients undergoing total hip or total knee replacement

Introduction

Dabigatran and rivaroxaban have recently been added to the armamentarium for thromboprophylaxis in orthopedic surgery. Although this is their first licensed indication, others will soon follow. Owing to their claimed predictable anticoagulant response that dispenses with the need for monitoring coagulation, their effects are poorly described in routine cases. However, interpreting blood coagulation results and evaluating whether a treatment is properly targeted in the case of untoward incidents will become a common concern for clinicians.

Methods

Eighty patients undergoing total hip or knee replacement were included in two studies. Forty of them received dabigatran (study 1) and 40 rivaroxaban (study 2). Blood samples (n = 176 and 166) were taken preoperatively and twice a week from the first postoperative day.

Results

Dabigatran increased aPTTr about two-fold and PT about 1.2-fold, and it was mostly an initiation-phase modulator of thrombin generation. Mean circulating concentrations as measured by a diluted thrombin time were 105±85 ng/mL at T_max in samples from patients receiving the full dosing. They depended significantly on renal function, body weight and gender.Rivaroxaban increased aPTTr and PTr around 1.5 fold and modified the initiation and amplification phases of thrombin generation, with a lowered and prolonged thrombin burst. Mean circulating concentrations as measured by an antiXa test were 117 ± 78 ng/mL at T_max.With both drugs, routine coagulation tests, thrombin generation curves and functionally determined concentrations exhibited high interindividual variability.

Conclusion

Routine coagulation tests are altered in patients receiving dabigatran or rivaroxaban, but their alterations poorly reflect the circulating concentrations as determined by functional approaches.     

A novel anti-platelet peptide (Z4A5) potential for glycoprotein IIb/IIIa inhibits platelet aggregation

Introduction

Z4A5 is a novel peptide that inhibits platelet aggregation and formation of platelet thrombi, but the mechanism of its anti-platelet effects remains unknown. This study explores the anti-platelet effect and mechanism of Z4A5.

Methods

We investigated the anti-platelet activity of Z4A5 on platelet aggregation induced by adenosine diphosphate (ADP), arachidonic acid (AA) and thrombin (TH) in human platelet-rich plasma (PRP). Fibrinogen and PAC-1 binding to glycoproteinIIb/IIIa (GPIIb/IIIa) were measured by flow cytometry. In addition, we investigated the integrin specificity of Z4A5 in attachment and detachment assays using human umbilical vein endothelial cells (HUVEC) and assessed the relative cell number using the MTT assay.

Results

In vitro, Z4A5 inhibited ADP-, AA- and TH-induced human platelet aggregation with IC₅₀ values of 0.46 ± 0.05 μM (n = 10), 0.23 ± 0.05 μM (n = 10) and 0.21 ± 0.02 μM (n = 10), respectively. Z4A5 inhibited fibrinogen, and PAC-1 bound to platelet GPIIb/IIIa with IC₅₀ values of 0.48 ± 0.07 μM (n = 8) and 0.63 ± 0.12 μM (n = 6), respectively. Z4A5 failed to inhibit α_Vβ₃ integrin-mediated HUVEC attachment to vitronectin and did not cause any significant detachment of HUVEC monolayer when compared with the controls.

Conclusions

Z4A5 is a potential anti-platelet drug that inhibits fibrinogen binding to GPIIb/IIIa, but does not affect the structurally similar integrin α_Vβ₃.     

Inhibition of the renin-angiotensin system downregulates tissue factor and vascular endothelial growth factor in human breast carcinoma cells

Introduction

The renin-angiotensin system (RAS) promotes angiogenesis and growth of neoplastic cells. Angiotensin-converting enzyme (ACE) inhibitors and angiotensin II receptor AT1 blockers may protect against cancer. Tissue factor (TF), for its involvement in tumor growth, angiogenesis, and metastasis is considered a hallmark of cancer progression.In this study we evaluated whether RAS blockade modulates TF constitutive expression by the metastatic breast carcinoma MDA-MB-231 cell line.

Materials and Methods

Cell TF activity was assessed by one stage clotting time, TF and VEGF antigens and mRNA levels by ELISA and RT-PCR, respectively. AT₁ was detected by flow-cytometry and angiotensin-II levels by EIA.

Results

Captopril reduced in a concentration-dependent way both the strong constitutive TF activity (983.2 ± 55.2 vs. 686.7 ± 135.1 U/5 × 10⁵ cells with 10 μg/ml captopril) and antigen (32.3 ± 5.9 vs. 13.2 ± 6.6 ng/ml) in MDA-MB-231. Similar results were observed with enalapril.AT1 was present on cell membrane and losartan, a competitive inhibitor of AT1, reduced TF expression to a degree similar as that exerted by ACE inhibitors. Moreover, captopril and losartan downregulated the constitutive mRNA TF expression by ~ 35%. Similar results were observed with anti-AT1 and angiotensin II antibodies. In addition, the constitutive VEGF antigen and mRNA levels were reduced in the presence of captopril or losartan, and an anti-VEGF antibody downregulated cell TF activity by ~ 40%.

Conclusions

These results could, at least in part, contribute to the discussion about the possible effects of ACE inhibitors and AT1 receptor antagonists in malignancy, and offer new clues to support their use for tumor control.     

Increased heparanase level and procoagulant activity in orthopedic surgery patients receiving prophylactic dose of enoxaparin

Background

Orthopedic hip and knee surgeries are followed by a hypercoagulable state. Heparanase is implicated in inflammation, coagulation activation and angiogenesis. Recently, heparanase was shown to directly interact with tissue factor (TF) and to enhance the generation of factor Xa (Nadir et al., Haematologica, 2010). In addition, an assay assessing heparanase procoagulant activity has been lately developed (Nadir et al., Thromb Res, 2011). In the present study heparanase level and procoagulant activity in patients undergoing orthopedic surgery were assessed.

Methods

The study group included 50 orthopedic patients. 31 patients underwent hip surgery and 19 had knee operation. 15 individuals suffered from traumatic hip fractures and 35 had osteoarthrosis of hip or knee joints. All patients received prophylactic dose of enoxaparin starting 6-8 hours post operation and lasting for 5 weeks. Plasma samples were drawn preoperatively and at 1 hour, 1 week and 1 month post operation. Samples were tested for heparanase levels by ELISA and TF/heparanase complex activity, TF activity, heparanase procoagulant activity, factor Xa and thrombin levels using chromogenic substrates.

Results

Heparanase levels were significantly higher 1 hour and 1 week post operatively compared to preoperative levels (p < 0.05, p < 0.005, respectively). The most dramatic changes were observed in heparanase procoagulant activity reaching a 2 fold increase 1 week postoperatively and 1.7 fold increase 1 month after surgery (p < 0.0001, p < 0.0001, respectively). Levels of factor Xa and thrombin did not significantly change.

Conclusions

Heparanase is involved in coagulation activation of orthopedic surgery patients. Heparanase procoagulant activity is highest 1 week postoperatively and remains high 1 month after operation. Considering extending prophylactic anticoagulant therapy or evaluating heparanase procoagulant activity may potentially prevent late thrombotic events.     

Anticoagulation therapy with combined low dose aspirin and warfarin following mechanical heart valve replacement

Introduction

This study was designed to evaluate safety and efficacy of combined low dose aspirin and warfarin therapy following mechanical heart valve replacement.

Methods

A total of 1 496 patients (686 males, mean age 35 ± 8.5 years) undergoing mechanical heart valvular replacement were randomly divided into study (warfarin plus 75-100 mg aspirin) or control (warfarin only) group. International normalized ratio (INR) and prothrombin time was maintained at 1.8-2.5 and 1.5-2.0 times of the normal value, respectively. Thromboembolic events and major bleedings were registered during follow up.

Results

Patients were followed up for 24 ± 9 months. The average dose of warfarin in the study and control group was 2.92 ± 0.87 mg and 2.89 ± 0.79 mg, respectively (p > 0.05). The overall thromboembolic events in study group were lower than in control group (2.1% vs. 3.6%, p = 0.044). No statistically significant differences were found in hemorrhage events (3.5% vs. 3.7%, p > 0.05) or mortality (0.3% vs 0.4%, p > 0.05) between the two groups.

Conclusions

Following mechanical valve replacement, combined low dose aspirin and warfarin therapy was associated with a greater reduction in thromboembolism events than warfarin therapy alone. This combined treatment was not associated with an increase in the rate of major bleeding or mortality.     

Plasma factor VII: a potential marker of pre-eclampsia

Introduction

Normal pregnancy is associated with a local hypercoagulable state that becomes more profound in certain obstetric complications such pre-eclampsia (P-EC). Current literature on the levels of individual haemostatic factors in women with P-EC is limited and results are inconsistent. In this study we provide detailed investigation on the tissue factor (TF)-dependent pathway in women with P-EC.

Materials and Methods

Enzyme-linked immunosorbent assays (ELISA) were used to measure plasma factor (F) FVII, FVIIa, TF and tissue factor pathway inhibitor (TFPI) in healthy non-pregnant women (n = 22), normal pregnant women (n = 15), and women with P-EC (n = 20). All subjects were age matched. In addition, pregnant women were matched for gestational age, parity and were all at the third trimester.

Results

Plasma FVII levels were significantly higher in women with P-EC compared to the healthy non-pregnant (P < 0.001) or the normal pregnant groups (P < 0.001). No such significant trends were observed for plasma FVIIa, TF or TFPI levels. Plasma FVII levels can distinguish women with P-EC from healthy non-pregnant women or normal pregnant women at the third trimester, with high sensitivity (90%), specificity (80%), positive and negative predictive values (86%).

Conclusions

Plasma FVII levels are significantly elevated in women with P-EC, in the absence of comparable changes in other TF-dependent pathway factors (FVIIa, TF and TFPI). We propose the use of plasma FVII as a marker for P-EC.     

Markers of endothelial and platelet activation are associated with high on-aspirin platelet reactivity in patients with stable coronary artery disease

Introduction

Aspirin inhibits the cyclooxygenase-1 (COX-1) mediated thromboxane A2 synthesis. Despite COX-1 inhibition, in patients with coronary artery disease (CAD), platelets can be activated through other mechanisms, like activation by thrombin.

Materials and Methods

At baseline in this cross-sectional substudy of the ASCET trial, 1001 stable CAD patients, all on single aspirin treatment, were classified by the PFA100® method, as having high on-aspirin residual platelet reactivity (RPR) or not. Markers of hypercoagulability, endothelial and platelet activation as related to RPR, were evaluated to explore the potential mechanisms behind high on-aspirin RPR.

Results

Altogether, 25.9% (n = 259) of the patients were found to have high on-aspirin RPR. S-thromboxane B₂ levels were very low and did not differ between patients having high on-aspirin RPR or not. Patients with high on-aspirin RPR had significantly higher levels of von Willebrand Factor (vWF) (124 vs 100%, p < 0.001, platelet count (236 vs 224 × 10⁹/l, p = 0.008), total TFPI (68.4 vs 65.5 ng/ml, p = 0.005) and ß-thromboglobulin (ß-TG) (33.3 vs 31.3 IU/ml, p = 0.041) compared to patients with low on-aspirin RPR. No significant differences between the groups were observed in levels of endogenous thrombin generation (ETP), pro-thrombin fragment 1+2 (F1+2), D-dimer, soluble TF (sTF) or P-selectin (all p > 0.05).

Conclusions

The high on-aspirin RPR as defined by PFA100® seems not to be due to increased thrombin activity as evaluated with ETP, sTF, F1+2 or D-dimer. The elevated levels of platelet count, ß-TG, TFPI and especially vWF might be explained by increased endothelial and platelet activation in these patients.     

Automated mixing studies and pattern recognition for the laboratory diagnosis of a prolonged activated partial thromboplastin time using an automated coagulation analyzer

Introduction

The objective of this study was to explore whether an automated coagulation analyzer could be applied to normal plasma mixing studies for the assessment of blood samples showing a prolonged activated partial thromboplastin time (APTT).

Materials and methods

Ten laboratory staff members performed normal plasma mixing studies and evaluated plasma samples using 3 different methods: (1) manual dilution and analysis, (2) manual dilution and automatic analysis with STA-R^®, and (3) automatic dilution and analysis with the Coapresta^® 2000 (CP2000). The time from the start of the analysis to the generation of the result plots and the plasma volumes required were determined. We analyzed patient plasma samples showing a prolonged APTT using the CP2000, and the result plots were categorized into 3 curve patterns based on the area ratio values: the inhibitor type (convex pattern), deficiency type (concave pattern), and suspicious inhibitor type (approximately straight pattern).

Results

When pooled patient plasma was used, the same patterns were obtained from normal plasma mixing studies using the 3 different methods. The time required to complete the mixing studies and the plasma volumes required were 28.2 ± 2.4 min and 350 μL for manual analysis, 23.2 ± 2.1 min and 875 μL for STA-R^®, and 8.5 ± 0.1 min and 175 μL for CP2000, respectively. Of 31 patient samples, 9 were categorized into the inhibitor type, 15 were categorized into the deficiency type, and 7 were categorized into the suspicious inhibitor type.

Conclusions

The CP2000 analyzer is applicable to the laboratory diagnosis of a prolonged APTT using pattern recognition, as it requires a shorter time to complete mixing studies and a smaller plasma volume in comparison with manual analysis.     

The relationship between plasma and placental tissue factor, and tissue factor pathway inhibitors in severe pre-eclampsia patients

Objective

To investigate the mechanism underlying the hypercoagulable state in severe pre-eclampsia.

Methods

Plasma tissue factor (TF) and tissue factor pathway inhibitor (TFPI) expression from pre-eclampsia patients and healthy pregnant controls were determined by ELISA. Placental TF and TFPI gene and protein expression were detected by quantitative RT-PCR, immunohistochemistry, and Western analysis.

Results

The plasma TF level in the pre-eclampsia group was significantly higher than the control group (p < 0.01), and surprisingly, the plasma TFPI-1 and TFPI-2 in the pre-eclampsia group were significantly lower (p < 0.01). Placental TF gene and protein expression levels in the pre-eclampsia group was significantly higher than the control group, while TFPI-1 and TFPI-2 levels were significantly lower (p < 0.05). Lastly, a significant correlation was found between plasma and placental TF protein levels in the pre-eclampsia group (p < 0.01).

Conclusion

Higher expression and/or release of TF from the placenta may contribute towards a pathological hypercoagulable state in pre-eclampsia patients.